Water pump pulley question

[CheyLadd]

I am in the process of upgrading my ARA aftermarket ac system. As part of that process I went to a sanden compressor and a new bracket. The new bracket and pump is going to require a 2 groove water pump pulley. My stock pulley is just over 7 inches in diameter and a single groove. I have searched high and low and cannot find a 7" 2 groove pulley for a short water pump. My question is, how much is a 6" pulley going to slow down my water pump and fan. I am very hesitant to do this because even though I have never had cooling issues, I am now going to be increasing temps due to having an ac running. Is a 6" going to work?

Truck is a 72 k10 short bed. Mild built 350 with a manual trans. New 4 core radiator, normal k10 shroud and a non clutch stock fan.